PL/SQL6——异常处理(Exception)

 Exception是一种PL/SQL标识符，当运行的PL/SQL块出现错误或警告，则会触发异常处理。为了提高程序的健壮性，可以在PL/SQL块中引

入异常处理部分，进行捕捉异常，并根据异常出现的情况进行相应的处理。

 

一、异常的类型 

    ORACLE异常分为两种类型：系统异常、自定义异常。

    其中系统异常又分为：预定义异常和非预定义异常。

 

    1.预定义异常

        ORACLE定义了他们的错误编号和异常名字，常见的预定义异常处理Oracle常见的错误

   

        NO_DATA_FOUND          SELECT ... INTO ... 时，没有找到数据

        DUL_VAL_ON_INDEX       试图在一个有惟一性约束的列上存储重复值

        CURSOR_ALREADY_OPEN    试图打开一个已经打开的游标

        TOO_MANY_ROWS          SELECT ... INTO ... 时，查询的结果是多值

        ZERO_DIVIDE            零被整除

 

    2.非预定义异常

        ORACLE为它定义了错误编号，但没有定义异常名字。我们使用的时候，先声名一个异常名，

        通过伪过程PRAGMA EXCEPTION_INIT，将异常名与错误号关联起来。

 

    3.自定义异常

        程序员从我们业务角度出发，制定的一些规则和限制。

 

二、异常处理

    PL/SQL中，异常处理按个步骤进行：

        定义异常

        抛出异常

        捕获及处理异常

 

    a.定义异常

        exception_name EXCEPTION;

 

    b.抛出异常

        RAISE exception_name

 

    c.捕获及处理异常

        EXCEPTION

            WHEN e_name1 [OR e_name2 ... ] THEN

                statements;

            WHEN e_name3 [OR e_name4 ... ] THEN

                statements;

                ......

            WHEN OTHERS THEN

                statements;

        END;

        /

 

 

三、异常处理示例   

    1.预定义异常的例子

        --演示一个整除的异常

            DECLARE

                v_n1 NUMBER:=50;

                v_n2 NUMBER:=0;

                v_n3 NUMBER;

            BEGIN

                v_n3:=v_n1/v_n2;

                DBMS_OUTPUT.PUT_LINE('v_n3='||v_n3);

            EXCEPTION

                WHEN ZERO_DIVIDE  THEN

                    DBMS_OUTPUT.PUT_LINE('v_n2 don't is 0');       

            END;

            /

       

        --演示VALUE_ERROR(错误号ORA-06502)

            scott@ORCL> declare

              2  v_ename varchar2(3);

              3  begin

              4      select ename into v_ename from emp where empno=&eno;

              5      dbms_output.put_line(v_ename);

              6  exception

              7      when value_error then

              8      dbms_output.put_line('variable datatype length is small');

              9  end;

             10  /

            Enter value for eno: 7788

            old   4:     select ename into v_ename from emp where empno=&eno;

            new   4:     select ename into v_ename from emp where empno=7788;

            variable datatype length is small

 

            PL/SQL procedure successfully completed.       

       

        --演示TOO_MANY_ROWS(对应Oracle错误号ORA-01422)

            scott@ORCL> declare

              2  v_ename emp.ename%type;

              3  begin

              4      select ename into v_ename from emp where deptno=&dno;

              5  exception

              6      when too_many_rows then

              7      dbms_output.put_line('Too many rows are returned');

              8  end;

              9  /

            Enter value for dno: 10

            old   4:     select ename into v_ename from emp where deptno=&dno;

            new   4:     select ename into v_ename from emp where deptno=10;

            Too many rows are returned

 

            PL/SQL procedure successfully completed.           

       

    2.非预定义异常

        非预定义异常使用的基本过程

            a.定义一个异常名

            b.将异常名与异常编号相关联

            c.在异常处理部分捕捉并处理异常

       

        DECLARE

            e_deptid EXCEPTION;

            PRAGMA EXCEPTION_INIT(e_deptid,-2292);

        BEGIN

            DELETE FROM DEPT WHERE DEPTNO=10;

        EXCEPTION

            WHEN e_deptid THEN

                DBMS_OUTPUT.PUT_LINE('at sub table have record!');

        END;

        /

 

        DECLARE

            e_emp EXCEPTION;

            PRAGMA EXCEPTION_INIT(e_emp,-2291);

        BEGIN

            INSERT INTO EMP(empno,deptno) VALUES (7935,60);

        EXCEPTION

            WHEN e_emp THEN

                DBMS_OUTPUT.PUT_LINE('60 at table dept not exist');

        END;

        /  

 

    3.自定义异常

        自定义异常与Oracle错误没有任何关系，有开发人员为特定情况所定义的例外

        下面的例子中当输入empno为时，尽管该雇员编号不存在，但PL/SQL代码并未给出适当的提示

            scott@ORCL> declare

              2  e_integrity exception;

              3  pragma exception_init(e_integrity,-2291);

              4  begin

              5      update emp set deptno=&dno where empno=&eno;

              6  exception

              7      when e_integrity then

              8      dbms_output.put_line('The dept is not exists');

              9  end;

             10  /

            Enter value for dno: 20

            Enter value for eno: 1111

            old   5:     update emp set deptno=&dno where empno=&eno;

            new   5:     update emp set deptno=20 where empno=1111;

 

            PL/SQL procedure successfully completed.

 

        针对上述情况，可以使用自定义异常处理。

        对于自定义的异常处理需要显示的触发，其步骤如下

            a.定义异常(在declare部分进行定义)

            b.显示触发异常(在执行BEGIN部分触发异常，使用RAISE语句)

            c.引用异常(在EXCEPTION部分捕捉并处理异常)

       

        --对上面的例子，使用自定义异常来处理，代码如下：

            scott@ORCL> declare

              2  e_integrity exception;

              3  pragma exception_init(e_integrity,-2291);

              4  e_no_employee exception;

              5  begin

              6      update emp set deptno=&dno where empno=&eno;

              7      if sql%notfound then

              8          raise e_no_employee;

              9      end if;

             10  exception

             11      when e_integrity then

             12          dbms_output.put_line('The dept is not exists');

             13      when e_no_employee then

             14          dbms_output.put_line('The employee is not exists');

             15  end;

             16  /

            Enter value for dno: 20

            Enter value for eno: 1234

            old   6:     update emp set deptno=&dno where empno=&eno;

            new   6:     update emp set deptno=20 where empno=1234;

            The employee is not exists

 

            PL/SQL procedure successfully completed.       

       

        --下面的例子中，如果插入的工资少于，就抛出异常

            DECLARE

                v_sal emp.sal%TYPE;

                v_id emp.empno%TYPE;

                e_sal EXCEPTION;      --定义异常

            BEGIN

                v_id:=&inputid;

                v_sal:=&inputsal;

                INSERT INTO emp (empno,sal) VALUES (v_id,v_sal);

                IF v_sal<700 THEN

                    RAISE e_sal;      --捕捉异常

                END IF;

            EXCEPTION                 --处理异常

                WHEN e_sal THEN

                    ROLLBACK;

                    DBMS_OUTPUT.PUT_LINE('Sal must be more than 700'); 

            END;

            /

           

四、使用异常函数处理异常           

    1.SQLCODE与SQLERRM函数

        函数SQLCODE用于取得Oracle错误号

        函数SQLERRM用于取得与错误号对应的相关错误消息

            scott@ORCL> get /u01/bk/scripts/sqlcode_errm.sql

              1  undef v_sal

              2  declare

              3      v_ename emp.ename%type;

              4      begin

              5          select ename into v_ename from emp

              6          where sal=&&v_sal;

              7          dbms_output.put_line('Employee Name:'||v_ename);

              8  exception

              9      when no_data_found then

             10          dbms_output.put_line('The employee is not exists for salary '||&v_sal);

             11      when others then

             12          dbms_output.put_line('Error No:'||SQLCODE);

             13          dbms_output.put_line(SQLERRM);

             14* end;

            scott@ORCL> start /u01/bk/scripts/sqlcode_errm.sql

            Enter value for v_sal: 1600

            old   5:         where sal=&&v_sal;

            new   5:         where sal=1600;

            old   9:         dbms_output.put_line('The employee is not exists for salary '||&v_sal);

            new   9:         dbms_output.put_line('The employee is not exists for salary '||1600);

            Error No:-1422

            ORA-01422: exact fetch returns more than requested number of rows

 

            PL/SQL procedure successfully completed.   

 

    2.RAISE_APPLICATION_ERROR

        是将应用程序专有的错误从服务器端转达到客户端应用程序(其他机器上的SQLPLUS或者其他前台开发语言)。

        该函数用于在PL/SQL中定义错误消息，且只能在数据库端的子程序中使用(存储过程、函数、包、触发器)，不能在匿名块和客户端的

        子程序中使用

 

        使用方法

            RAISE_APPLICATION_ERROR(error_number,message[,{true | false}]);

           

            该函数内的错误代码和内容，都是用用户自定义

            error_number：用于定义错误号，且错误号从-20000 到-20999 之间，以避免与ORACLE 的任何错误代码发生冲突。

            message：用于指定错误消息，且消息长度不能超过k，超出部分将被截取

            可选参数true,false:默认值为false，会替换先前的所有错误。当设置为true，则该错误会被放在先前错误堆栈中。

           

            scott@ORCL> get /u01/bk/scripts/sp_raise_comm.sql

              1  create or replace procedure raise_comm

              2  (v_no emp.empno%type,v_comm out emp.comm%type)

              3  as

              4  begin

              5       select comm into v_comm from emp where empno=v_no;

              6       if v_comm is null then

              7           raise_application_error(-20001,'It is no comm for this employee');

              8       end if;

              9  exception

             10       when no_data_found then

             11       dbms_output.put_line('The employee is not exist');

             12* end;

            scott@ORCL> start /u01/bk/scripts/sp_raise_comm.sql

 

            Procedure created.

 

            scott@ORCL> variable g_sal number;

            scott@ORCL> call raise_comm(7788,:g_sal);

            call raise_comm(7788,:g_sal)

                 *

            ERROR at line 1:

            ORA-20001: It is no comm for this employee

            ORA-06512: at "SCOTT.RAISE_COMM", line 7

                       

            scott@ORCL> call raise_comm(7499,:g_sal);

 

            Call completed.

 

            scott@ORCL> print g_sal

 

                 G_SAL

            ----------

                   300     

 

五、PL/SQL编译警告

    1.PL/SQL警告的分裂

        SEVERE: 用于检查可能出现的不可预料结果或错误结果,例如参数的别名问题.

        PERFORMANCE: 用于检查可能引起性能问题,如在INSERT操作是为NUMBER列提供了VARCHAR2类型数据.

        INFORMATIONAL: 用于检查程序中的死代码.

        ALL: 用于检查所有警告.

   

    2.控制PL/SQL警告消息

        通过设置初始化参数PLSQL_WARNINGS来启用在编译PL/SQL子程序时发出警告消息，缺省为DISABLE:ALL

        警告消息设置的级别

            系统级别

            会话级别

            ALTER PROCEDURE

            既可以激活或禁止所有警告类型,也可以激活或禁止特定消息号

            scott@ORCL> show parameter plsql%ings;

 

            NAME                                 TYPE        VALUE

            ------------------------------------ ----------- ------------------------------

            plsql_warnings                       string      DISABLE:ALL       

           

            scott@ORCL> ALTER SYSTEM SET PLSQL_WARNINGS='ENABLE:ALL' |'DISABLE:ALL'

            scott@ORCL> ALTER SESSION SET PLSQL_WARNINGS='ENABLE:PERFORMANCE' |'DISABLE:ALL'

            scott@ORCL> ALTER PROCEDURE usp COMPILE PLSQL_WARNINGS='ENABLE:PERFORMANCE';

            scott@ORCL> ALTER SESSION SET PLSQL_WARNINGS='ENABLE:SEVERE','DISABLE:PERFORMANCE','ERROR:06002';

   

    3.演示PL/SQL编译告警

        a.检测死代码

            在下面的代码中，ELSE子句永远不会执行,应该避免出现类似的死代码.

            从Oracle 10g开始,在编写PL/SQL子程序之前开发人员可以激活警告检查.

           

                scott@ORCL> get /u01/bk/scripts/dead_code.sql

                  1  CREATE OR REPLACE PROCEDURE dead_code AS

                  2     x number := 10;

                  3  BEGIN

                  4     IF x>0 THEN

                  5             x:=1;

                  6     ELSE             

                  7             x:=2;    --死代码

                  8     END IF;

                  9* END dead_code;

               

                scott@ORCL> start /u01/bk/scripts/dead_code.sql

               

                scott@ORCL> alter session set plsql_warnings='enable:informational';

               

                scott@ORCL> show parameter plsql%ings

 

                NAME                                 TYPE        VALUE

                ------------------------------------ ----------- ------------------------------

                plsql_warnings                       string      ENABLE:INFORMATIONAL, DISABLE:

                                                                 PERFORMANCE, DISABLE:SEVERE

                                                                 

                scott@ORCL> alter procedure dead_code compile;

 

                SP2-0805: Procedure altered with compilation warnings          

 

                scott@ORCL> show errors;

                Errors for PROCEDURE DEAD_CODE:

 

                LINE/COL ERROR

                -------- -----------------------------------------------------------------

                4/6      PLW-06002: Unreachable code

                7/3      PLW-06002: Unreachable code

       

        b.检测引起性能问题的代码

            scott@ORCL> create or replace procedure update_sal

              2  (no number,salary varchar2)

              3  as

              4  begin

              5      update emp set sal=salary where empno=no;

              6  end;

              7  /

 

            Procedure created.

 

            scott@ORCL> alter session set plsql_warnings='enable:performance';

 

            scott@ORCL> alter procedure update_sal compile;

 

            SP2-0805: Procedure altered with compilation warnings

 

            scott@ORCL> show errors

            Errors for PROCEDURE UPDATE_SAL:

 

            LINE/COL ERROR

            -------- -----------------------------------------------------------------

            5/24     PLW-07202: bind type would result in conversion away from column